1. Field of the Invention
This invention relates to a windshield wiper control system and more particularly to a wipe-after-wash circuit for continuing wiping of the windshield after washing for a plurality of wipe cycles to dry the windshield and then to park the wiper blade and arm assembly in an absolute park storage location each time the circuit is employed with consistent accuracy.
2. Description of the Prior Art
After washing with wash fluid while wiping the windshield to wash it, the washing ceases and the wiper blades continue to wipe the windshield until all the fluid is removed, drying the windshield. Then, the blade and arm assembly is returned to a park storage location.
A problem exists with some systems in returning the wiper arm and blade assembly to a storage location below the visible regions of the windshield. Often, the wiper blade returns to a position just above storage on the windshield and very visible to the operator instead of off the windshield in the park storage location. This problem generally occurs because some automatic wiping circuits are improperly timed to fully return the wiper blades to an absolute park storage location and sometimes system power or environmental conditions interfere.
U.S. Pat. No. 4,731,566 of Takaishi dated Mar. 15, 1988 entitled "Intermittent Drive Controller For Windshield Wiper Motor" teaches a wipe-after-wash terminated by braking the wiper at the moment that the wiper motor pauses. A braking loop circuit stops the wiper motor at one revolution after a dwell-type motor switch changes from a voltage source terminal to a ground terminal. This system effectively stops the wiper blades in a park location but it appears that the one revolution of the motor may not totally clear the windshield of the wash solution.
Another wipe-after-wash circuit is described in U.S. Pat. No. 4,158,159 dated June 12, 1979 of Orris, et al. entitled "Electronic Circuit Controller For Windshield Drive Motor" and assigned to the present assignee. In this patent, a reversible two-speed, three-brush, permanent magnet field DC motor drives the wiper motor. After a wash pushbutton is released, a timing network provides power to a transistor drive circuit which causes the reversible motor to operate for one or two cycles before the wiper blade is returned to a park location. The park location occurs within a span of 0 to 40 degrees; the zero location equalling a fully parked wipe blade while within a 40 degree position stops the blades somewhere within the vision of the operator. The environmental conditions such as dryness of the windshield and the power conditions of the electrical system, which could provide operating voltages ranging from 9 volts to as high as a possible 24 volts, could effect the timing circuit. The wiper motor could be stopped somewhere in the region between zero and 40 degrees without any guarantee of the blades returning to the absolute park position at zero degree.
Realizing the various problems associated with returning the wiper blade to an absolute park position, a search for various other means to achieve an absolute park position which could be integrated into an existing wash and wipe system was initiated. This search resulted in improved wipe-after-wash system of the present invention.